Facts About Mammals That Lay Eggs

Among the best characteristics of mammals that include the presence of hair or fur on the skin and mammary glands in the females that secrete milk is they give birth to their live young instead of laying eggs. However, there is and exception to this. Of the 21 orders of the Mammalia class, one order is so classified for the reproductive nature of its species to lay eggs rather than live births. This is the order Monotremata.

Only two families compose the order Monotremata: Tachyglossidae, where echidnas belong; and Omithorhynchidae, which has the platypus. Monotremes are found in Australia, including Tasmania, and New Guinea. A few, however, have been successfully bred outside of these countries, usually in zoological parks. A few animal collectors have managed to breed echidnas as backyard pets.

Also referred to as spiny anteaters, echidnas are best characterized by the spiky spines mixed with long, coarse hairs that cover their bodies. Their toothless mouth has a long sticky tongue suitable for picking ants and termites, their main diet. Echidnas inhabit a variety of shelters from rocks to woods, holes in the ground, small caves, or even under bushes. Though long-lived, echidnas have a low reproductive rate, for the female lays only a maximum of two eggs.

There are two popular species of echidnas. The short-beaked echidna (Tachyglossus aculeatus), found in Australia, is about 12 to 18 inches long, excluding its short tail. It has a small head and a nose that is extended into a slender snout. The curved-beak echidna of New Guinea (Zaglossus brukini), on the other hand, is distinct for its curved snout and can grow to a length of up to 30 inches. Smaller echidnas make useful pets, especially in places where ants and termites are such abundant pests. Despite their spiky body coverings, echidnas are known to be gentle and harmless animals unless threatened. Unfortunately, human activities are the primary causes of the diminishing echidna population. In places where they abound, hundreds of echidnas die every year due to vehicular accidents, forest fire, and purposeless butchery.

Because of its ambiguous characteristics, the platypus (Ornithorynchus anatinus) has fascinated scientists who have been studying it for years. In fact, the platypus was taken to be a hoax for a number of years after 1797, when it was first discovered. Some scientists during that time could not believe in a mammal that has some features of a duck—long, soft, leathery snout that looks like a beak, and webbed feet.

The platypus has short fur and a broad, flat tail. It shelters in burrows dug in the bank of rivers or streams, where the female also lays its eggs. Semiaquatic and nocturnal, it usually hunts for food in riverbeds during the night. Its food constitutes mainly of shellfish, shrimps, insect larvae, worms, tadpoles, and fish. Though the life span of the platypus exceeds 10 years, its reproductive rate is quite low. It lays only a maximum of four eggs. The adult male is well known for the presence of a hollow, horny claw on the ankle of each hind foot. Humans, who hunt them for their fur and for biological curiosities, are the chief enemies of the platypus. Fortunately, in Australia and in other countries where the platypus specie thrives, strict laws in protection of these duck-billed monotremes are well enforced.